The present invention relates to a magnetic thin-film head comprising a stratified build-up on a nonmagnetic substrate for a recording medium which is provided with a magnetizable storage layer into which information can be written along a track by perpendicular or vertical magnetization of the storage layer. Such magnetic heads have a ring-shaped magnetic conduction body for carrying the magnetic flux, the conduction body having two magnet legs, the poles of which facing the recording medium are arranged in tandem as viewed in the direction of motion of the head and at a predetermined spacing from each other. The turns of an at least largely flat write/read coil winding extend through a space formed between the magnet legs. See, e.g., European patent application EP No. 0 012 910 Al.
The principle of perpendicular magnetization for storing information is generally known. See, for instance, IEEE Transactions on Magnetics, vol. MAG-16, no. 1, Jan. 1980, pages 71 to 76; DE-OS 29 24 013; U.S. Pat. No. 4,287,544; or the cited European patent application. For this principle, which often is also called vertical magnetization, special recording media in the form of rigid magnetic discs, flexible individual discs (floppy discs) or magnetic tapes are required. Such a recording medium has at least one magnetizable storage layer of predetermined thickness which contains magnetically anisotropic material, especially of a CoCr alloy. The axis of the so-called easy direction of magnetization of this layer is directed perpendicularly to the surface of the medium. By means of a special magnetic head, the bits of information are then written along a track in successive sections, also called cells or blocks, by appropriate magnetization of the storage layer. In practice, the magnetic flux changes are generally used as information, i.e., the transition from one direction of magnetization to the opposite one. The sections have a dimension in the longitudinal direction of the track which is also called wavelength. This dimension can be substantially smaller than that required by the method of longitudinal or horizontal storage, which is given by the demagentization. Thus, the information density in the recording medium can be increased advantageously according to the principle of perpendicular magnetization.
The combined write and read heads, known for the principal of longitudinal magnetization, i.e., head types by which the write as well as the read function can be executed, however, cannot be used directly also for perpendicular magnetization. If these heads are used, which generally have a ring-head-like shape, the flux conduction desired also for a the principle of perpendicular magnetization to form a circuit closed as far as possible can be obtained with low magnetic resistance. However, difficulties arise with these ring heads when reading the written information.
One is therefore compelled to develop special write and read heads for the principle of perpendicular magnetization. Such a magnetic head has, in general, a so-called main pole, with which a vertical magnetic field sufficiently strong for changing the magnetization of the individual sections of the storage layer is produced. The necessary magnetic return can then take place, for instance, by a so-called auxiliary pole on the opposite side of the recording medium. See the mentioned literature reference, IEEE Trans Magn., vol. MAG-16. A magnetic return can further be accomplished by a special auxiliary pole which is located on the same side as the main pole. See IEEE Trans Magn., vol. MAG-17, no. 6, Nov. 1981, pages 3120 to 3122, or vol. MAG-18, no. 6, Nov. 1982, pages 1158 to 1163, or the above mentioned patent literature. Accordingly, the magnetic read and write head known from the mentioned European patent application contains a ring-head-like magnetic conduction body having two magnet legs which carry the magnetic flux and the ends of which, facing the recording medium, form a main and an auxiliary pole which are arranged in tandem as seen in the direction of motion of the head and which are arranged at a predetermined spacing from each other. The turns of an at least largely planar coil winding extend through a space which is formed between these two magnet legs, the space being filled with insulating materials. With this winding, the main pole is excited for the write function, and for the read function, the excitation of the main pole is recorded. The turns of this winding as well as the magnet legs are applied by a thin-film technique on a nonmagnetic substrate.
With the magnetic head type which is known, for instance, from the above mentioned patent references, the auxiliary pole should serve in any case only for the return of the magnetic flux. Possible concurrent writing of the auxiliary pole optionally can be tolerated because the recording main pole always lags it and therefore overwrites the information which may have been written by the auxiliary pole. However, in order to prevent concurrent reading of the auxiliary pole with its trailing edge at least to a large extent, the so-called air gap formed betwen the two poles would have to be relatively wide in order to assure a far-reaching reduction of the magnetic flux density at the auxiliary pole. Correspondingly wide gap layers however, can be realized only with difficulty by thin-film techniques.
Because of these difficulties, magnetic heads have already been proposed, in which the use of a separate auxiliary pole is dispensed with. See IEEE Trans. Magn., vol. MAG-18, no. 6, Nov. 1982, pages 1170 to 1172; EP No. 0 071 489 A2. In these magnetic heads, the necessary magnetic return is provided by the stray flux. Accordingly, the magnetic head known from the last mentioned European patent application contains substantially only a single magnet leg which faces the recording medium and which is associated with a planar write and read coil winding. With such a magnetic head type, which is also called a single-pole head, the requirements for an effective write function can generally be met, at least largely. Accordingly, a field strength sufficiently large for recording at high bit densities for reversing the magnetization of the storage layer of the recording medium is to be achieved and, on the other hand, the drop of the magnetic field at the trailing edge of the head should be as steep as possible so that small transition widths of the magnetization reversal can be realized. See IEEE Trans. Magn., vol. MAG-19, no. 5, Sep. 1983, pages 2239 to 2244. A sufficiently large read signal, however, cannot be obtained if the auxiliary pole is omitted.
Due to these mentioned problems in reading, systems with separate write and read heads are known so that these heads can be adapted optimally to the respective function. See IEEE Trans. Magn., vol. MAG-16, no. 5, Sept. 1980, pages 967 to 972 or vol. MAG-17, no. 6, Nov. 1981, pages 2538 to 2540. For the read function, the ring heads known per se from the principle of longitudinal magnetization can be used, while the write function must be carried out with the mentioned single-pole heads. These single pole heads each have an auxiliary pole on the back side of the recording medium. The design of similar systems, however, for reading and writing with special heads adapted to the respective function is relatively elaborate.